The aide said it was expected that Republicans would filibuster the 2011 National Defense Authorization Act, which provides funding for the Defense Department, and 60 votes would be needed to end debate on the bill and bring it to the Senate floor for a vote. GOP senator John McCain of Arizona renewed his filibuster threat last week.

Repeal advocates expressed optimism that they would find the necessary votes to send the legislation to the floor.

"We feel fairly confident that we will have the 60 votes to break a filibuster of the National Defense Authorization Act," said Alex Nicholson of the gay veterans group Servicemembers United. "This bill contains important provisions for all troops and important funding provisions for the entire military. It would be hard — and shameless — for lawmakers to hold up this critical bill because of opposition to one or two of its myriad smaller provisions."

Although some Democratic senators, such as Jim Webb of Virginia, might break with their party and support the filibuster, some Republican senators could help compensate for the deficit.

Sen. Richard Lugar of Indiana has already indicated he would not support a filibuster; Sen. Susan Collins of Maine voted for the repeal measure in the Senate Armed Services Committee and is a good candidate to also break with her party. Other GOP senators who might vote to break the filibuster include Olympia Snowe of Maine and Judd Gregg of New Hampshire.

Nicholson noted that no Democratic senator has given a strong indication to date that he or she would join a Republican filibuster.

What's less clear is what might happen if the bill reaches the Senate floor, where amendments might be offered to strike the repeal language or to expand the terms of the certification process beyond the president, Defense secretary, and chairman of the Joint Chiefs to also include the service chiefs of the Army, Navy, Air Force, and Marines. Either measure would require 51 votes to pass.

But Nicholson said there's still an element of the unknown in any calculation at this point.

"A lot of the vote estimations really come from pre-recess intelligence," he said, noting that senators just returned to Washington Monday. "I don’t think any organization has gotten a feel for how the August recess has impacted members positions on this issue."

Nicholson added that the decision in the Log Cabin Republican case, which found "don't ask, don't tell" unconstitutional, could also play a role in the mood on Capitol Hill.

"That was another huge nail in the coffin," he said. "It really drove home for people that the writing is on the wall."